Answer: Roses are susceptible to a number of foliar diseases including rust, which might account for the discoloration. Check the undersides of the affected leaves for rust pustules. If none are found, you may be dealing with downy mildew (the yellowing will stay between the veins of the leaves), verticillium, leaf burning due to overfertilization, or even overwatering. We've had a cool and rainy summer this year, which may have stressed the plants or at least contributed to their ill-health. If possible, take a sample to your local Extension office or Master Gardener clinic for a positive ID of the problem. You can contact King County Cooperative Extension at (206) 296-3900. Hope this helps solve the mystery!
Q&A Library Searching Tips